This is the version that you would need to change: https://github.com/openmrs/openmrs-core/blob/2.2.0/pom.xml#L282
After doing so, confirm that you can successfully compile. Get an instance of the latest reference application and replace its platform war file with the one you have compiled. Run and do some basic testing to confirm that all is well. Try to do a fresh setup of OpenMRS to see if all is good. Try an upgrade from a lower platform version to the one you compiled to see if all is still fine.
You may also need to update these liquibase extensions: https://wiki.openmrs.org/display/docs/Liquibase+Extensions